1. Field of the Invention
The present invention relates to a stabilizer platform for a moving object such as a vehicle or a vessel and, more particularly, to a stabilizer platform carrying a satellite dish antenna wherein the antenna is continuously pointed at a target satellite by controlling only the azimuth and elevation of the antenna to compensate for movement of the vessel.
2. Statement of the Problem
The popularity of programming received from a satellite has significantly increased over the past decade. Today, digital programming is being delivered by a number of different companies using satellites to transmit signals to earth-based small satellite dishes such as dishes 18 inches in diameter. In most instances, the consumers install the small satellite dish antennas at a fixed geographic site such as at their home. Some consumers install small satellite dish antennas on top of their vehicles such as a recreational vehicle. When they park the vehicle, they tune in the desired satellite.
A need exists to permit vehicles that are moving such as recreational vehicles (RVs), marine vessels and floating sea platforms to continuously lock into a target satellite even though the vehicle or vessel moves in different directions. This is accomplished by mounting a stabilizer platform providing rapid alignment between the satellite dish antenna targeted on the satellite and the moving vehicle.
Vessels pose a particular problem especially in a heavy sea. When a vessel moves in water, the direction may change (yaw), the vessel may tilt along the length (pitch), or the vessel may tilt from side to side (roll). Hence the stabilizer platform must rapidly compensate for changes in yaw, pitch and roll to maintain the small satellite dish antenna targeted on the satellite. In addition, the stabilizer platform must be capable of rapid alignment so as to maintain the integrity of the received signal from the targeted satellite.
Prior art stabilizer platforms are of many types. One mechanically simple type is the two axis amount termed the AZ-EL mount which controls the dish antenna in the azimuth (AZ) and elevation (EL) directions. Such AZ-EL mounts typically use a turntable that may be rotated about the azimuth axis and a support that can be elevated about an elevation axis. AZ-EL mounts can be quickly and accurately pointed to any target in the sky. By rapidly moving the turntable about the azimuth axis and in the elevation axis, these stabilizer systems can compensate for yaw, pitch and roll of the vessel.
A problem with AZ-EL stabilizer platforms occurs when the cables that connect to the dish antenna and to the azimuth and elevation motors wrap around components of the system during use. A need exists to have a design that eliminates this wrap problem.
A need exists for an AZ-EL stabilizer platform that has the azimuth and elevation motors mounted to the base of the stabilizer platform so as to eliminate the wrapping problem for the electrical cables.
When the control motors are placed on the moving part of the stabilizer platform, not only does it add to the weight of the moving part but often additional weight must be added to counterbalance to weight of the motors. A need exists to eliminate the added weight from the motors on the moving part and the added weight from counterbalancing.
In certain prior AZ-EL platforms, the AZ and EL driver must be activated separately. A need exists for an AZ-EL drive system wherein both drives can be activated simultaneously.
Finally, it is a goal of the present invention to provide singularity of control for the AZ and EL axes so that, for example, the stabilizer platform can be rotated through 360.degree. turns in the same direction without wrapping of the cables.
A patentability search was directed toward the features of the present invention and this search resulted in the following patents.
The "Two Access Mount Pointing Apparatus" (published Oct. 13, 1994, as International Publication No. WO 94/23469) patent application discloses a pointing arm carrying a satellite dish antenna mounted to a universal joint supported by a base on a ship. The pointing arm is rotatably mounted within the universal joint for rotation about first and second control axes. The universal joint provides rotation of the point arm through greater than 180 degrees but less than 360 degrees about each of the first and second control axis while suffering no singularities of control.
U.S. Pat. No. 3,599,495 relates to a stabilizing platform using a three axis gimbal system including a gyroscopically stabilized platform.
U.S. Pat. No. 3,999,184 provides a platform having elevation, azimuth, roll and pitch motors. The cable control lines for the motors are designed with slack to provide elevation travel of at least 90 degrees and azimuth travel of at least 270 degrees.
U.S. Pat. No. 4,197,548 sets forth an antenna stabilizing system using three linear hydraulic actuators for pitch, yaw and roll connected on the mount. Independent elevational positioning of the antenna is provided.
U.S. Pat. No. 4,586,050 sets forth an automatic tracking system for an antenna using an electronic control connected to roll and pitch sensors for controlling the AZ and EL drives. The antenna also uses a tracking system for locking onto a satellite. The AZ and EL drives are alternatively driven.
U.S. Pat. No. 4,821,047 discloses a mechanical analog of the geosynchronous satellite arc and then forces the axis of the antenna to rotate through the geosynchronous arc.
U.S. Pat. No. 5,223,845 sets forth an AZ-EL system for controlling azimuth and elevation of an array antenna. The array antenna is pivotally supported on an azimuth axis frame by an elevation axis. The elevation axis motor is mounted on the azimuth axis fram. U.S. Pat. No. 5,227,806 is related to the aforesaid patent.
U.S. Pat. No. 3,355,954 teaches the use of three gyroscopes and motors mounted to rotating gimbals to obtain a stabilized platform.
None of the prior art approaches set forth the mounting of the elevation and azimuth motors on the non-moving support base of the stabilizer platform or deliver the signal cable through the center of the platform so as to eliminate cable wrap.
Solution to the Problem
The present invention provides a stabilizer platform for a satellite dish antenna that eliminates wrapping of the motor control and power lines. This is achieved without use of expensive slip rings or rotary joints. The present invention places the elevation and azimuth motors on the base of the stabilizer platform which is fixed to the surface of the vessel or vehicle. The placement of the motors on the base eliminates motor wrap with respect to the control and power cables attached to each motor. The signal cable from the satellite dish antenna is passed through the center of the stabilizer platform. The placement of the motors on the base also eliminates the requirement for use of counterweights on the moving parts of the stabilizer platform. Both the azimuth and the elevation control motors can operate on the satellite dish simultaneously.